It depends on the mobile phone you have and whether you are willing to question anti-consumerist principles for technology!
If you have a smartphone most can be used as a wifi hotzone to link to the Internet but most people don't as they either dont know you can or they wont as most carriers charge for Internet use - however if you get the oneplan from 3 and a smartphone that does the business (my iPhone does it - sorry technology is my weakness) you can run your laptop on the Internet using their 3G network- the oneplan gives unlimited Internet use over 3G plus free calls/texts - I don't know if other providers do a similar deal but you could shop around
However i don't know how sustainable it would be nor how frustrated you would get with the speeds as 3G can be slooooow.
Obviously if you dont use/use minimally your Mobile it wont be worth the outlay. But if you were the type to have a geeky smartphone you may as well get what you can back from the companies that squeeze us!
Btw I'm a teacher not a mobile phone expert/salesperson!